Wrecking ball
A wrecking ball is a heavy steel ball, usually hung from a crawler crane, that is used for demolishing large buildings. It was most common from the 1930s to the 1970s. Several wrecking companies claim to have invented the wrecking ball. An early documented use was in the breaking up of the SS Great Eastern in 1888-9, by Henry Bath and Co, at Rock Ferry on the river Mersey. With the invention of larger hydraulic excavators and hydraulic attachments & machinery, the wrecking ball has become less common at demolition sites because its working efficiency is smaller compared to that of long reach excavators. Although the wrecking ball is still an efficient way to raze medium to large brick structures, it is decreasing in use, in the western world. This is mainly due to H&S rules and a lack of skilled operators. Construction and design Modern wrecking balls have had a slight re-shaping, with the metal sphere changed into a pear shape with a portion of the top cut off. This shape allows the ball to be more easily pulled back through a roof or concrete slab after it has broken through. Wrecking balls range from about 1,000 lb to around 12,000 lb (450 kg to 5400 kg). The ball is made from forged steel, which means the steel is not cast into a mold in a molten state. It is formed under very high pressure while the steel is red hot (soft but not molten) to compress and to strengthen it. Early users often just used concrete blocks but they were unsuitable for tougher material like reinforced concrete & could break up. Method of use To demolish roofs and other horizontal spans, the ball is typically suspended by a length of steel chain attached to the lifting hook of a crane boom above the structure, the rope drum clutch is released and the ball is allowed to free-fall onto the structure. To demolish walls the ball is suspended at the desired height from a crane boom and a secondary steel rope pulls the ball toward the crane cab. The lateral rope drum clutch is then released and the ball swings as a pendulum to strike the structure. Another method for lateral demolition is to pivot the crane boom to accelerate the ball toward the target. This is repeated as needed until the structure is broken down into debris that can easily be loaded and hauled away. The demolition action is carried out entirely through the kinetic energy of the ball. Modern equivalents The first demolition excavators were created by attaching along pole to the bucket of a crawler loader or to the boom of a hydraulic excavator & pushing structures up to 4 stories over. This saved bring in a crawler crane & ball on most smaller job sites, as the machine could do 2 jobs rather than one. Next hydraulic hammers and hydraulic grabs were used and fitted to longer and longer arms on a modified excavator leading to the creation of the high reach machine that today top 60m + which is more than most crawler crane and ball machines could reach. These machines can cut steel beams up to 2 m deep & sort the scrap out as they go saving secondary sorting, were as a wrecking ball just smashes it into a big heap. Other alternatives The advancement of technology led to the development and use of blasting charges, safer than dynamite and more efficient or practical than wrecking balls, to destroy buildings. The most common use of blasting charges is to implode a building, thus limiting collateral damage; see Demolition. Wrecking balls are more likely to cause collateral damage, because it is difficult to completely control the swing of the ball. Current applications A version of the wrecking ball is still used in quarries for breaking oversize rocks up were blasting is restricted or the use of hydraulic hammers exceed noise limits. They are also used for breaking up concrete slabs such as runways & roadways. See also * Demolition equipment * Construction plant References / sources based on a wikipedia article External links Category:Tools Category:Demolition Category:Construction equipment Category:Glossary